1. Field of the Invention
The invention is a multiple reflections interferometer having two cooperative mirrors that form an effective wedge, to increase the displacement sensitivity.
2. Description of the Prior Art
The most common instrument for measuring small mechanical motions and vacuum deposit coatings has been the Michelson interferometer which produces one cycle of signal change for a movement or optical thickness change of .lambda./2 where .lambda. is the wavelength of the laser being used as the light source. In this type interferometer, one of its two mirrors remains fixed while the other mirror undergoes movements, or displacements. As the mirror moves, the interference signals go through several cycles of intensity. The mirror displacement is determined simply by counting the number of detected output cycles. By using the Standard Michelson Interferometer (SMI), the cycle counting technique does not work for displacements less than approximately .lambda./4, which produces an output at the detector of one-half of a cycle. Further, cycle counting accuracies are typically limited to about one-tenth count which restricts the accuracy to about .lambda./20 mirror displacement.